Holding furnace particularly for vacuum diecasting apparatus

ABSTRACT

A holding furnace, particularly for a die-casting apparatus, comprising a bucket which can be heated, is adapted to contain molten material and is provided with a lid which can be opened and is shaped substantially like an inverted cup; the lid is provided with at least one opening for introducing protective gas having a higher relative density than air and adapted to generate an atmosphere for protection from contact with air for the molten material at regions that are free from the containment means walls of the bucket.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a holding furnace particularly for a die-casting apparatus.

[0002] In the die-casting process, the main step consists in injecting a specific amount of molten metallic material in a die; optionally, in the case of vacuum die-casting, this is done after producing a vacuum inside the die.

[0003] In terms of plant maintenance and amortization costs, the die-casting process is highly advantageous if it relates to the production of large batches meant for high-volume mass-manufacturing lines.

[0004] The recent trend is to use light alloys to produce castings to be used as structural elements and/or components, such as for example car chassis and body parts of assembly-line vehicles.

[0005] Standard die-casting apparatuses, however, are scarcely suited for the production of vehicle frame or body components due to their brittle fracture behavior and to the porosity of the resulting castings.

[0006] It is in fact currently impossible to produce Al—Mg alloy castings, because such castings are full of porosities, with a high number of inclusions of gas and impurities.

[0007] Brittle fracture, porosity and inclusions are unacceptable in castings which should be welded and which are required, in various forms, to have high plastic deformation properties.

[0008] The main causes of the above mentioned problems are the very structure and geometry of the parts that constitute standard die-casting apparatuses.

[0009] Before injection into the die, the molten material is retained in a holding furnace.

[0010] The holding furnaces currently in use are substantially constituted by containment bowls in which the molten material is kept at a constant temperature.

[0011] However, the material contained in the furnace is in contact with contaminating atmospheres constituted for example by air, consequently generating oxides and forming inclusions of gas inside the casting.

[0012] Moreover, slag is sometimes present on the containment walls of the furnace and may compromise the purity of the casting and therefore its final mechanical characteristics.

SUMMARY OF THE INVENTION

[0013] The aim of the present invention is to provide a holding furnace whose structure is such as to solve the above noted problems observed in conventional holding furnaces.

[0014] Within this aim, an object of the present invention is to provide a furnace having such a structure that the molten material never makes contact with contaminating atmospheres or slag.

[0015] Another object of the invention is to provide a furnace which allows to work in a protective gas atmosphere.

[0016] Another object of the invention is to provide a holding furnace having a particularly simple structure.

[0017] This aim and these and other objects and others which will become better apparent hereinafter are achieved by a holding furnace, particularly for a die-casting apparatus, characterized in that it comprises a bucket which can be heated, is adapted to contain molten material and is provided with a lid which can be opened and is shaped substantially like an inverted cup, said lid being provided with at least one opening for introducing a protective gas having a higher relative density than air and adapted to generate an atmosphere for protection from contact with air for said molten material at regions that are free from the containment means of the bucket.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

[0019]FIG. 1 is a sectional view of a furnace according to the present invention;

[0020]FIG. 2 is a plan view of a portion of a die-casting apparatus in which a furnace having the structure according to the invention is used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] With reference to the figures, a holding furnace according to the invention is generally designated by the reference numeral 10.

[0022] The furnace 10 is constituted by a substantially hollow body 11 which contains a bucket 12 for containing molten metallic material.

[0023] Heating elements 13 are provided on internal walls of the body 11 and are adapted to maintain the temperature of the molten material contained in the bucket 12.

[0024] The containment bucket 12 is provided with a lid 14 which is substantially shaped like an inverted cup and in which a protective gas, advantageously nitrogen, is contained which is adapted to generate an atmosphere for continuous protection against contact with air for the material contained in the bucket 12, at the surface that is not affected by the containment walls of the bucket 12.

[0025] Since nitrogen is a gas which is heavier than air, the danger of contact between air and molten material, and therefore the generation of oxides which generate inclusions, is eliminated both when the lid 14 is closed and when it is open.

[0026] The lid 14 is provided with openings 15 for introducing the protective gas and with openings for placing probes 16 which are adapted to detect the physical characteristics of the gas.

[0027] In this case, the probe 16 is a thermocouple which detects the temperature of the gas.

[0028] The bucket 12 further has rounded walls which follow the revolving motion of a mixer 17 which allows to clean and degas the molten material.

[0029] Moreover, the rounded walls facilitate the cleaning of any slag by virtue of corresponding cleaning means, which are not shown in the figure but are in any case of a per se known type.

[0030] The lid 14 can of course be opened to allow the insertion of the mixer 17 and the loading of the molten material.

[0031] In a die-casting apparatus it is possible to use two holding furnaces 10 a and 10 b mounted on a turntable 18.

[0032] The turntable 18 is circular and the two furnaces 10 a and 10 b are mounted in diametrically opposite positions.

[0033] Means for moving the turntable are associated with the turntable 18 and also comprise a motor 19.

[0034] In a region below the turntable 18, at the floor, there is a duct 20 in which protective gas flows; the gas arrives from a station, not shown in the figure, and flows toward the inlets 15 a and 15 b of the corresponding holding furnaces 10 a and 10 b.

[0035] When the furnace 10 b is located at the mixer 17, the corresponding lid 14 b opens to allow the insertion of the mixer 17 and the loading of the material by means of the loading channel 21.

[0036] The mixer 17 is then removed from the furnace 10 b, the lid 14 b is closed, and the turntable 18 turns until the furnace 18 b is in the position that is occupied in FIG. 2 by the furnace 10 a, from which the molten material is taken in order to be loaded into injection units, not shown, of the die-casting apparatus.

[0037] At this point, it is the furnace 10 a that is subjected to the cleaning and degassing operation by means of the mixer 17 and to loading with new molten material.

[0038] In practice it has been observed that the present invention has achieved the intended aim and objects.

[0039] A holding furnace has been in fact provided which allows to keep constantly in contact with a protective gas atmosphere the regions that are not affected by the means for containing the molten material.

[0040] Accordingly, one of the main problems of using light alloys, such as Al—Mg alloys, in standard and innovative die-casting apparatuses is eliminated if a holding furnace having the structure according to the invention is used.

[0041] The technical details may be replaced with other technically equivalent elements.

[0042] The materials, so long as they are compatible with the contingent use, as well as the dimensions, may be any according to requirements.

[0043] The disclosures in Italian Utility Model Application No. PD2000U000046 from which this application claims priority are incorporated herein by reference. 

What is claimed is:
 1. A holding furnace, particularly for a die-casting apparatus, comprising a bucket which can be heated, is adapted to contain molten material and is provided with a lid which can be opened and is shaped substantially like an inverted cup, said lid being provided with at least one opening for introducing a protective gas having a higher relative density than air and adapted to generate an atmosphere for protection from contact with air for said molten material at regions that are free from the containment walls of the bucket.
 2. The furnace according to claim 1 , wherein said lid is provided with at least one probe for detecting at least one physical characteristic of the protective gas.
 3. The furnace according to claim 2 , wherein said at least one physical characteristic to be detected is the temperature of the protective gas.
 4. The furnace according to claim 1 , wherein said protective gas is nitrogen. 